Types
Builtin Primitive data types; native to most hardware Note: not objects (will use mostly first four) byte (1 byte = 8 bits) boolean (1bit) short (2 bytes) int (4 bytes) long (8 bytes) double (8 bytes) char (2 bytes) float (4 bytes)
Primitive Types (base types)
Constants/Literals (by example):
boolean f = false; int i = 32769; double d = 0.333333; char c = 'x';
CompSci 6
byte b = 33; short s = 21; long l = 289L; float = 3.141592F;
5.1
Named Constants
Probably should name most constants
Use the final keyword
Should have no "Magic Numbers" in program By convention, use all caps in the identifier
Keeps you from accidentally changing value; final boolean CORRECT = true; final int SQUAD_SIZE = 12; final double MIN_GPA = 2.5; final char FAIL = 'F'; final String AUTHOR = "Dietolf Ramm";
Note Constants provided by Java: (from API) Math.PI, Math.E, Integer.MAX_VALUE
CompSci 6 5.2
Arithmetic Operators
Arithmetic
Increment/Decrement
o +, -, *, /, % (remainder or mod) o e.g., k++, k-- , ++k, --k o <, <=, ==, !=, >=, > o Used only for numbers except == and != o For boolean only: !, &&, || o "I'm " + 19 + " years old and live in " + city o variable = expression o variable op= expression o ( shorthand for: variable = variable op expression )
Logical (results in boolean value)
String Concatenation Assignment
CompSci 6
5.3
Operators
Arithmetic
Increment/Decrement
+, -, *, /, % (remainder or mod) Work for both integers and reals Except watch / and % integers for o What is 13/5 ? 13%5 ? 3/5 ? 3%5 ? e.g., k++, ko Written as
Can write code like
k++;
not
k = k++;
!!
Usually not a good idea: confuses. Use a separate line for increment of p.
5.4
k = 3 * p++ - m / 5;
CompSci 6
Operators
Combining Assignment and Arithmetic
variable op= expression ( shorthand for: variable = variable op expression ) Thus the following lines contain equivalent statements
k = k 1; q = q * r; s = s / 2;
k -= 1; q *= r; s /= 2;
k--;
CompSci 6
5.5
Assignment
(Familiar by now) x = 13.3; k = k + 7; area = 2.0 * Math.PI * radius * radius;
Casting: (type) int k = 3; double t; t = k; // OK, No information lost int m; double s = 3.5; m = s; // ILLEGAL, information lost CompSci 6 (accidentally?) m = (int) s; // OK, information lost
Vocalize as "gets" or "becomes" Don't use "equals": Not Equality
5.6
Casting
Implicit Casting
Types...